Electric motors commonly produce a rotational output, but many mechanisms require that a linear movement be driven by the motor. A leadscrew drive is one approach for translating the rotational movement of the motor to the required linear movement. In the conventional leadscrew drive, the thread of an externally threaded leadscrew engages a recirculating ball nut structure, which in turn is connected to the structure to be driven linearly. As the leadscrew turns, the ball nut structure and the driven structure move linearly.
This conventional leadscrew drive is relatively expensive to produce due to the precision machining required. It is also limited to relatively large-size devices and coarse thread pitches because of the size of the balls used in the recirculating ball nut structure. The conventional leadscrew drive may be subject to excessive wear of the threads, particularly if there is any misalignment. The conventional leadscrew drive also requires careful alignment between the motor, the leadscrew, and the driven structure because of the mechanical engagements at each end of the leadscrew. Another major disadvantage of the conventional leadscrew in light-duty and medium-duty applications is that it has far more strength than is needed, and is quite heavy. The resulting high rotational mass gives the leadscrew a high inertia, adversely affecting its ability to accelerate and decelerate rapidly.
An advance in overcoming some of these disadvantages is described in U.S. Pat. No. 5,636,549, whose disclosure is incorporated by reference. The '549 patent discloses a leadscrew in which the thread structure is defined by a wire wound helically around a cylindrical shaft. A leadscrew-nut assembly is also disclosed for engaging the leadscrew to the linear slide assembly.
The approach of the '549 patent is useful for many applications, but it still has a greater mass and rotational inertia than desired for some applications. There is always a need for a leadscrew drive that has reduced mass, while retaining sufficient strength. The present invention fulfills this need, and further provides related advantages.